Rabu, 21 Januari 2009

Between men and women, dyslexia takes sides

More than 30,000 neuroscientists from around the world gathered in Washington, D.C., November 15–19 for the annual meeting of the Society for Neuroscience. Presentations covered the science of nerves and brains on scales from molecules to societies.

Offerings the second day of the meeting, November 16, are sampled here: surprising insights about the brain on age, one of the first studies to investigate the brains of dyslexic women, a new finding about head trauma, and details on how the skin senses touch.

Dyslexia’s female twist

Women’s brains have a different read on dyslexia than men’s brains do. Women diagnosed with this severe disability in reading and other facets of written language show a right-brain deficit in tissue volume, in contrast to a primarily left-brain volume reduction already reported for dyslexic men, according to a team led by neuroscientist Guinevere Eden of Georgetown University in Washington, D.C.

Tissue volume provides one sign of neural function. Until now, researchers have only studied the neural basis of dyslexia in men and in mixed-sex groups that contained only a minority of women.

Eden’s group used an MRI scanner to examine brain volume in eight women who had dealt with dyslexia since childhood and eight women with no reading or language problems. Participants ranged in age from 19 to 25. Dyslexic women exhibited a relative reduction of tissue volume in part of the right parietal lobe. It’s hard to know how this brain area relates to reading, says study coauthor Tanya Gerner, a Georgetown neuroscience graduate student

“This finding stands in stark contrast to volume reductions in the left temporal lobe reported previously for dyslexia in males,” Gerner says.

The team also studied brain volume in girls with dyslexia. Nine school-age girls ages 7 to 13 and diagnosed with dyslexia displayed reductions in tissue volume not just in one brain area, but in a variety of areas, compared with eight girls of the same age group who had no reading problems. Earlier studies have observed comparably widespread reductions in neural volume among dyslexic boys, relative to their male peers who have at least average reading ability.

It appears that boys and girls with dyslexia start out with similar types of neural volume deficits that diverge by adulthood to different sides of the brain, Gerner says. The reason remains unclear, she adds. As dyslexic boys and girls receive special reading instruction throughout schooling, their brains may compensate for initial reading difficulties in sex-specific ways, she theorizes. —Bruce Bower

Anatomy of the brain that ages well

People who are mentally vigorous at age 80 can have more plaques in their brains than their normal-aging counterparts. At the same time, these higher-performing brains hosted fewer tangles, which are denser, more harmful clumps of proteins.

Plaques are diffuse clumps of proteins in the brain, and clumps of the protein beta-amyloid are often associated with Alzheimer’s disease. The finding could spur research into possible benefits of having plaques, says study leader Changiz Geula. One guess is that plaques may serve as safe repositories for harmful proteins that would otherwise float around in the brain, Geulaadds.

The surprising preliminary finding comes from a new study called the SuperAger Project, which departs from the traditional way of studying the aging brain. Instead of examining the brains of people who suffer from age-related diseases such as Alzheimer’s and Parkinson’s —what Geula calls “shrinkers”— the team wants to figure out what happens in the brains of people who age well. “We want to know what can be learned from these brains,” says Geula, of Northwestern University.

His team examined brains of 14 elderly high-performers called superagers. They qualified by showing cognitive ability equal to that of a 50-year-old, having been cognitively stable for at least three years, or by achieving at least one major life accomplishment, such as writing and publishing a book, after age 80.

The study’s goal is to identify many features of superaging brains, such as which genes and molecules may be important for mental agility at older ages. These features could lead to clues about why some people stay so sharp for so long.

The SuperAging Project is in its infancy: Geula calls the study’s sample size of 14 “puny,” but these types of in-depth studies on brains that surpass expectations may lead to new understanding of the aging process, he says. —Laura Sanders

Protein could stop post-trauma brain swelling

Brain swelling following an injury is anything but swell. It can lead to damaged tissue and, in some cases, the resulting pressure can lead to death.

Scientists hunting for ways to prevent swelling—which occurs when water accumulates in brain cells—have recently turned to a small protein called erythropoietin. Produced naturally in the body, the protein has been long known for its role in blood cell production, but erythropoietin may also prevent water uptake by brain cells, reports Eli Gunnarson of the Karolinska Institutet in Stockholm, Sweden.

After a brain injury, ions and other molecules can accumulate inside cells, a build-up that spurs water accumulation. Water can enter brain cells through a channel known as aquaporin 4. Experiments by Gunnarson’s team with cell cultures and excised brain tissue showed erythropoietin lessened the amount of water taken up by the cells. And in experiments with mice whose brains were overloaded with water, treatment with erythropoietin reduced swelling significantly more than a salt solution did.

Gunnarson’s team thinks that erythropoietin may prevent the aquaporin 4 channel from opening by interfering with calcium ions, which give the aquaporin channel the go-ahead to open.

Erythropoietin is already given to people as treatment for specific diseases such as anemia. Gunnarson says it’s a promising treatment for cell swelling, if its action can be localized. “The mechanisms of cell swelling are quite complicated,” she says. —Rachel Ehrenberg

Good vibrations

The fast-adapting “touch receptor” that alerts the brain when someone brushes by you, and allows elephants to pick up on vibrations from miles away, is now touching off new interest from scientists.

Pacinian corpuscles, small onion-shaped receptors in the skin, are first in line to pick up sensations and transmit messages to the brain. Those corpuscles were long thought to be activated by mechanical means. New findings show that these receptors can also talk to neurons through the release of chemical agents.

The corpuscles are composed of a delicate nerve ending surrounded by a helmet-like capsule. The portion of the capsule that sits next to the nerve develops from Schwann cells, a type of glial cell associated with other types of touch receptors in the body. Scientists had believed that the receptor’s ability to pick up signals was due to the mechanical properties of its helmet-like capsule.

Lorraine Pawson of Syracuse University in Syracuse, N.Y., and collaborators isolated PC receptors from cats and then stimulated the receptors with a tiny probe for one-half to four seconds. The researchers then added an agent to block GABA, a messenger chemical known to suppress nerve impulses. Those and further experiments showed that the capsule can signal the nerve chemically, probably with molecules from the glial cells.

“Typically, scientists think of glial cells as packing peanuts, cells that are there to protect or support the nerve, “ says one of Pawson’s collaborators, Adam Pack of Utica College in New York. “These findings show that these cells are actively responding by releasing neurotransmitters.”